I went through the undergrad medical course (UNSW) some time back, so probably can't help you out on actual GAMSAT too much.

Feel free to message/post me if any wishes to discuss anything general eg. which textbook is good for what subject in uni, general hints and tips about internship, hospital residency etc. Anything I know I'd be glad to answer.

Please check out also my forum (gpland . org) if you got time. Non-commercial. Just a fun forum for doctors or people who want to become doctors to talk about anything casually, plus a chatroom and some multiplayer games if you get too bored in the library.